Hi! I am trying to compare changes from 2007-2009 to 2010-2012. Therefore, I merge ACS multi-year datasets for 2007-2009 and 2010-2012. I ran logit regressions in Stata with and without using weights, and the coefficient for the variable year changed substantially. To be clear, I used the syntax “logit i.year i.DV. predictors… [pw=perwt]” to apply weights. For unweighted regression, I simply dropped “[pw=perwt]”. In the weighted regression, the year variable is highly significant and positive, but in the unweighted regression, the year variable is negative and not significant (p=0.445).

Why is there such a big difference? Which result is right? When pooling data from multiple ACS datasets, can we still apply year-specific/dataset-specific weights in the pooled sample? BTW, I know I should have also used replicate weights, but I did not… I have the same question, how can we apply replicate weights if we pool multiple ACS datasets?

Thank you!!!

Yue